1. Field of the Invention
The present invention relates to an orifice plate mounted inside a hydraulic engine mount using magnetorheological (MR) fluid, and more particularly, to an orifice plate formed so that a magnetic field is aligned perpendicularly to the flow direction of MR fluid across all regions of the flow path through which the MR fluid flows, and so that the flow path allows only a unidirectional flow along the perimeter of a coil assembly at the inside and outside, respectively, of the coil assembly.
2. Description of the Related Art
In order to dampen engine vibrations, the engine of a vehicle is mounted in the engine room of the vehicle body through engine mounts. Engine mounts that are commonly used are rubber mounts employing the resilience of rubber material, and hydraulic mounts that are filled with liquid and use viscous resistance from the movement of the liquid to dampen vibrations.
Of these, the hydraulic engine mount is configured to dampen vibrations in both a high frequency range and a low frequency range, and are widely used in many types of vehicles.
FIG. 1 illustrates a cross-section of a hydraulic engine mount having a conventional structure. The hydraulic engine mount holds hydraulic fluid in an inner space defined by an insulator 2 and a diaphragm 7, and the inner space has an orifice plate 4 installed therein and is partitioned into an upper liquid chamber 3 and a lower liquid chamber 6.
The orifice plate 4 has a flow path 5 along an inner perimeter thereof for hydraulic fluid to flow through, and has a decoupler selectively mounted in the center thereof. A stud bolt 1 coupled to the insulator 2 is coupled to an engine bracket. Thus, the insulator 2, formed of a resilient material, is repeatedly compressed and restored resiliently by changes in load and vibrations exerted on the stud bolt 1, and the hydraulic fluid flows through the flow path 5 in the upper liquid chamber 3 and the lower liquid chamber 6. This flow of the hydraulic fluid vibrates the decoupler, and vibrations in a high frequency range are dampened through vibrations of the decoupler, and vibrations in a low frequency range are dampened through the flow of hydraulic fluid through the flow path 5.
The hydraulic mount may be filled with MR fluid instead of a general hydraulic fluid. Magnetorheological (MR) fluid is a suspension having smooth, magnetic particles mixed in synthetic hydrocarbon liquid, and has the property of shear stress that varies according to whether a magnetic field is applied nearby and the intensity of an applied magnetic field.
Accordingly, an orifice plate 4′ of a hydraulic mount filled with MR fluid, as illustrated in FIG. 2, has a flow path 5′ formed vertically therein, and a coil 8 further installed to apply a magnetic field near the flow path 5′ through which MR fluid passes. By controlling the amount of current applied to the coil 8, the dynamic stiffness and the damping characteristics of a mount are rendered controllable according to the conditions in which a vehicle travels.
When a magnetic field is not applied, the MR fluid exhibits flow properties similar to a general hydraulic fluid, but when a magnetic field is applied nearby, the particles are aligned in columns to change the flow characteristics of the fluid.
Specifically, the shear stress of the MR fluid is determined as a value that is a multiple of viscosity and shear rate when a magnetic field is not applied, and when a magnetic field is applied, the shear stress of the MR fluid becomes the value (of the multiple of the viscosity and the shear rate) to which a yield shear stress is added. The yield shear stress increases proportionally to the intensity of the applied magnetic field.
As illustrated in FIG. 2, in order to align the particles inside the MR fluid perpendicular to the flow direction, the direction in which the magnetic field is applied should be perpendicular to the flow direction of the MR fluid.
In related art methods, however, while a magnetic field is aligned perpendicular to the flow direction of MR fluid in region “A” and region “C” in a structure in which a coil is disposed a certain distance apart from a side of a flow path, the magnetic field in region “B” is formed in a parallel direction (to the flow direction of the MR fluid) and does not pass through the MR fluid, which thus lowers controlling efficiency.
While the lowered controlling efficiency can be restored by raising the value of the current applied to the coil or forming a longer flow path, this involves the limitation of an increase in size, which increases the amount of heat generated.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.